1. Field of the Invention
The present invention relates to magnetic disk drives, and more particularly, to self-servowriting of tracks on a rotating magnetic disk medium.
2. Description of the Related Art
The writing of servo track information on a magnetic disk medium is a critical process in the manufacture of a disk drive. Conventionally, servo track information is written with a specialized servowriting instrument mounted on a large granite block to minimize external vibration effects. Increasing track densities and decreasing disk size has led to the investigation of self-servowriting techniques.
In self-servowriting, the read head track-follows on a track and writes the servo information for a subsequent track, which then becomes the reference track for the next track. The process is repeated until all servo tracks are written. When a conventional Phase Locked Loop (PLL) compensator is used, errors arise due to amplification of spindle harmonics and other timing disturbances of similar frequency spectrum in the written track due to the peaking nature of the closed-loop transfer function. Thus, there is a need for technique for reducing phase or timing error propagation during self-servowriting.